RAID is an acronym for Redundant Array of Independent Disks, and it’s a core feature of server hardware that ensures data integrity. It’s also just a fancy word for two or more hard disks connected together to add some additional functionality. Why would you want to do this? Read on.

RAID Configurations

First off, it’s very difficult to describe RAID technologies as a whole, because the different configurations available to you create very different functionalities – but they all focus on either speed or reliability. Let’s break them down:

RAID 0: Striped

This configuration is all about speed. In short, data is spread across a number of disks (striped across the disks, in fact) – rather than being written to just one. This overcomes speed limitations of a single drive, so performance is theoretically multiplied by the number of disks you are using.

It’s a similar concept to having 4 cores in your CPU – instead of sequentially writing instructions to one CPU, you send different parts of it to 4 different CPUs, and get the answers back 4 times as quickly. You also get to use the combined space of all of the drives, so 2 x 1TB in a striped configuration will show as a single 2TB drive.

On the downside, you also have as many points of failure as drives you are using – if just one of those drives fails, all your data will be lost. In reality then, this configuration is rarely used. If the data isn’t so valuable though, you might want to set up a RAID0 on a home server or even a desktop machine.

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RAID 1: Mirrored

This configuration is all about data integrity and is far easier to explain. In a RAID 1 setup, data is mirrored to the other drives – a full backup of everything is kept at all times, because the bits of data are simultaneously written to different drives, at the same time. Because of this, you only get the total drive space of a single drive, so 2 x 1TB drives set up to mirror each other will only give you 1TB total space.

This is perhaps the most common real world usage when two disks are available. When one dies, the data is still 100% there and ready for use, but the process of “re-building” the data array on the replacement drive can take a very long time.

RAID 0+1: Striped & Mirrored

This combines the best of both worlds by nesting RAID setups, but requires at least 4 disks. 2 sets of 2 striped disks are then set up, each set replicated to the other. RAID 1+0 also exists, but doesn’t vary enough to warrant a separate explanation – it’s a case of striping your mirrors rather than mirroring your stripes!

RAID 2 & Above: Parity Bits

With 3 disks, you can actually achieve a good performance and integrity compromise by using what is called a parity disk. To explain this, think on a scale of bits instead of whole drives.

A parity bit is simply an XOR combination on the other bits. XOR is a logic operation that evaluates to true if only ONE of the two input bits is true. See the following table, where P is the parity bit.

A B P
0 0 0
0 1 1
1 0 1
1 1 0

Now it turns out that this is very useful for error checking and repairing the data. If you were to erase the entire B column, you could rebuild it simply because you still have both the parity bit and A, and given those then there is only one possible answer for bit B.

Now, it should be easy to see that even if we had 2 x 1 terabyte drives worth of bits, we could still create a parity for every single bit and place it on a 3rd drive that’s also a terabyte in size. And that’s RAID3. With a 3 disk array, 2 are used to stripe the data, spreading it out for performance. The 3rd drive creates a parity set, and if any one of those drives dies, we can use the other 2 to recover it in full.

I won’t go into details about RAID 3, 4, 5 and 6 because they’re basically all variants on where and how parity bits are stored or derived, and precisely how much recovery can be done. If you’d like to read up on those, I’d suggest the extensive Wikipedia page on the topic.

Can I Use RAID On My Home PC? Should I?

Both OSX and Windows have the ability to create software RAID configurations, but bear in mind that this is going to increase the load on your operating system due to the additional computation required. I won’t go into setting them up here, but if you’d like to know more or see a tutorial on MakeUseOf, let me know in the comments and I’ll get straight on it.

A lot of motherboards also include a form of semi-hardware RAID – I say semi-hardware, because they generally still need a driver in your OS to be able to access the data, but this is still one step up from a purely software RAID, and you can even install the OS onto them for a small performance boost.

The final method of doing RAID is with dedicated hardware – upgrade cards that you can slot into your PC and take full control of the data side of things. These are of course the most reliable and best performing, but the price range is generally out of consumer budgets.

As for whether you should be using a RAID, it’s certainly worth playing around with for geek points. In terms of real world computing, the performance gains you can expect are often less than the trouble involved (an SSD would far outperform them anyway), or the data redundancy you gain can be easily achieved with other traditional backup methods.

Check out the other Technology Explained articles for more fascinating insights into the technologies behind computers and the Internet.

I'd be iffy about that. Yes, RAID1 mirrors your drive. But it also mirrors any mistakes or deletions. And if your system is stolen or (potentially) has a hardware issue, you risk losing both.

Now, if you set up a NAS - sure, mirror those drives, while using backup software to *do* the backup from your PC to the NAS. But don't just assume RAID1 is "a backup." It *can* save your bacon, sure, if just one drive fails. But there are a lot of situations where a (local, to be clear) RAID1 doesn't help.

Work out a "real" backup solution - even if it's just running backup software and an external drive.

Tux sounds like a person you would want to avert having a discussion or difference of opinion about any subject. Do not confuse Tux with facts...his mind is already made up. Maybe he should place his brain in gear before his mouth goes into motion. What a tool !!!!!!!!!!!

Because as I stated in the article, the only thing that differentiates them is the precise algorithm for placing data and parity information. This article is supposed to be a beginner level introduction to the technology of RAID, not a in-depth technical definintion of the various types of RAID in commercial use.

"Both OSX and Windows have the ability" .. blah. "Both?"Linux, BSD's, all other variants also have this and available from the get-go when installing the system. Also along with RAID one can have LVM and encryption, everything done smoothly and configured easily. Can't say the same for win/osx."but bear in mind that this is going to increase the load on your operating system"With today's systems it's really negligible, even on systems with atom processors encrypted raids are fine."motherboards also include a form of semi-hardware RAID"You invented this term yourself, when the standard way is to call it what it is - fakeraid.Software raid done via a sluggish chip. Nothing more."data redundancy you gain can be easily achieved with other traditional backup methods."RAID is NOT a backup.It is meant to keep the system running without interruption in case of a hardware failure and to have the chance to replace the broken drive(s) without losing data and having to restore from backups, which one should have even with RAIDed system, of course.As said, installing two drives in RAID1 when setting up a new system does not involve any trouble at all. Just a few options and everything will be taken care of.Please, try and see for yourself, eg. by installing Debian, Ubuntu or FreeBSD.

Thanks for your input Tux, you certainly aren't wrong. However, a very small minority of our readers use linux on the desktop (less than 5% in fact), and even less use BSD. Neither are suitable operating systems for any kind of entry level user, but that's an entirely different discussion I don't want to go into here. If linux works for you, then great, but please don't get annoyed when it isn't talked about as a major operating system that's significant in the home user market, because it isn't.

I think you invented the term "fakeraid", to be honest! You said yourself it's performed via a slow (hardware) chip, so I think my term semi-hardware is quite suitable.

You're right though - RAID should not ever be used in place of a real 'backup' system, but arguing over semantics isn't the point of this article either. I mentioned it from a users perspective, because most users would consider a redundant RAID setup to be a backup - yet it isn't, and other methods are better.

"Neither are suitable operating systems for any kind of entry level user"

I disagree strongly.Many linux distributions are suitable for any kind of new or inexperienced user, and I have plenty of proof for it. Apathy against real alternatives and unwillingness to learn (both equal to laziness) are the only real reason why adoption hasn't been better. Oh and not to mention force-feeding windogs with almost all new computers."so I think my term semi-hardware is quite suitable"Of course, for you, since you came up with it. Nobody really uses that term, believe me.Let's do a simple googlefight, shall we?"semi-hardware" +raid = 3990 hits"fakeraid" +raid = 118000 hitsAnd please, go read the pages that use term fakeraid and you'll finally see.

"because most users would consider a redundant RAID setup to be a backup - yet it isn't,"

Then it certainly isn't about semantics. You should bluntly say yourself that it isn't a backup solution, instead of telling it is.

Unwillingness to learn, eh? I really don't think an operating system is something the average user should be forced to "learn". They shouldn't need to consult a forum when their wifi doesn't connect; they shouldn't need to read a guide to figure out how to install software. Apathy to move *away* from familiar windows is a good reason perhaps, but I'd argue strongly against linux still being anyway near the level of user-friendliness that OSX has. Right now you DO need a manual for ubuntu or whatever other flavour of the month linux is popular.

Oh, and "semi-hardware" alone gets 97 million results - Fakeraid gets 192,000. I'll use whatever terms I like in my own article - feel free to apply at the next call for writers though, as it'd be great to have another linux pro on the team to bring your knowledge to the world.

As for semantics, ITIL defines a backup as " Copying data to protect against loss of Integrity or Availability of the original." - a mirrored RAID setup fulfils this definition and can therefore be considered a backup. Easy.

Can we stop this now? I'm sorry I didn't talk about linux in my article, it was an unconscious decision just as I also didn't include IRIX, BSD, os/2, or any other non user-level OSes. I don't have anything against those OSes, nor people who use them, but I'm not going to write about them.

James has a BSc in Artificial Intelligence, and is CompTIA A+ and Network+ certified. He's the lead developer of MakeUseOf, and spends his free time playing VR paintball and boardgames. He's been building PCs since he was a kid.